1. Field of the Invention
The present invention relates to an apparatus and method for measuring transmitted light, reflected light, phosphorescence, or luminescence from a substance to examine physical properties, superficial condition, or compositional state of the substance.
2. Description of the prior Art
Aiming at surpassing conventional electronics, there have been introduced recently new techniques of molecular electronic devices and bio-chips wherein a molecule or an assembly of a small number of molecules functions as an electronic element. Among such new techniques, the method of forming a film of monomolecular layer(s) draws attention as a technique of organizing a highly ordered laminar assembly of molecules. This method comprises transferring a monomolecular layer formed on a wafer surface onto a solid surface, or building up such monomolecular layers one by one over a solid surface, thereby forming an ultra thin film. According to this method, the components and structure of the composite film can be freely designed. In order to evaluate absorption spectra of coloring matter in such monomolecular films, an extremely slight change in transmittance must be detected and therefore special photometric apparatuses are in use.
FIG. 5 illustrates such a photometric apparatus according to the prior art. In operating this apparatus, a sample held in a sample cell 3 is irradiated through a spectroscope 2 with a light beam from a light source 1 while oscillating the sample 4 in the direction perpendicular to the light beam by means of an oscillation regulating unit 5, the transmitted light is received with a photomultiplier unit 6, and the resulting photoelectric currents are integrated in phase with the oscillation period of the sample. Further, in FIG. 5, 7 is a PSD (phase sensitive detector), 8 a recorder, and 9 a wavelength presetter.
The prior art photometric apparatus, however, has a drawback in that the information obtained therewith represents only average properties (e.g. physical properties) of the sample in the scanning range of the light beam spot on the sample and not of those in individual microscopic areas of the sample, for example, the difference in a specific distribution or aggregation of coloring matter between microscopic areas of the sample. Now that each microscopic area is observed, it is meaningless unless a very minute change in the sample can be detected, particularly when the sample is a monomolecular film or the like. With simple amplification of signals due to microscopic areas, accurate measurement of such a change is impossible due to the effects of noise. In addition, while the light beam is desired to be as narrow as possible for the purpose of evaluating each microscopic area, it is difficult to converge the light beam sufficiently since the light beam passing through the spectroscope is spread by a prism or the like.
According to the monomolecular film forming method, it is possible to design and construct a mixed monomolecular film consisting of two or more kinds of molecules or a hetero built-up film consisting of monomolecular layers which are different in composition. An important technique for evaluating physical properties of these ultra thin films is to detect unevenness between microscopic areas of the film surfaces. For instance, it is known that in mixed monomolecular films of a merocyanine colorant substituted by a long-chain alkyl and a long-chain alkylcarboxylic acid (e.g. arachidic acid), monomers, dimers, and further J-associates of the merocyanine are present, and the distribution state of these components affects properties of the film. Therefore, the distribution state that these components are placed in, and the change in the distribution state that occurs depending on the film thickness, are interesting matters in the evalution of physical properties of the film. However it is the present situation that information about such matters cannot be obtained as stated above with the photometric apparatus according to the prior art.